Rainbow Parrotfish

(Scarus guacamaia)

The Rainbow Parrotfish is the largest parrotfish and the largest herbivorous fish in the Caribbean Sea.
They can grow to a maximum length of 1.2m and a weight of 20kg. 
The large males are brightly colored, particularly green and orange; the head, fins and tail are bright orange while the back is bright green. However, females and small males are dull colored.
The teeth of the parrotfish are clustered together, forming a tough mouthpiece that looks like a parrot’s beak, where its name was derived. They also possess a pharyngeal apparatus where teeth are seen in rows, found in the throat and specialized to disintegrate food.

Juvenile

Initial Phase​

Terminal Phase

Habitat and Distribution

The rainbow parrotfish has a relatively wide distribution in the western Atlantic, and can be found from Bermuda through South Florida, the Bahamas and the Caribbean to Venezuela. It inhabits coral reefs, mangroves and sea grass beds in shallow waters, at depths of 1–25 meters.

Diet and Behavior

The rainbow parrotfish are at the herbivore trophic level. They mostly get food in the coral reefs, with their diet consisting mainly of algae, seaweed and organic matter from the coral surfaces. 
Its specialized teeth aid in the process of scraping algae off the coral surfaces. 
The newly hatched larvae begin to feed after three days but it is uncertain as to how long this stage lasts. 
Also, they may form large groups in order to go feeding in an attempt to ward off predators.

Reproduction

The individuals in this species must undergo three distinct phases within the life cycle. 
The first phase consists of sexually immature juveniles, which have a characteristic drab colour. 
The second phase is called the Initial Phase and consists of sexually mature males and females.
The final Terminal Phase consists of only mature males that are brightly coloured.

The rainbow parrotfish have a very complex system of reproduction.
They live in a harem group, whereby one single terminal male is dominant in a group of females.
This dominant male mates with the females in the group, and deters other male competition.
The species is diandric, meaning that the population includes primary and secondary males.
A primary male was born that sex. However, a secondary male is a fish born female, that transforms into a male.
This transformation of a female fish to a male fish occurs upon the death of a Terminal Phase male. His death signals the largest Initial Phase female to undergo morphological and behavioural changes, transforming into a male.
“Sneak spawning” may also occur, where Initial Phase males disguise themselves as a female in an attempt to enter the harem.
At peak spawning, they release a cloud of gametes in an attempt to overwhelm the fertilisation by the Terminal Phase males. They are adapted for this process, as they have larger testes than the Terminal Phase male, therefore producing more gametes than the latter.
This increases their chance of fertilising the female.

Conservation Status

The Rainbow Parrotfish was formerly classified as vulnerable due to overfishing and habitat loss, but because the presently available data do not allow an estimate of the population decline, it is now considered near threatened by the IUCN. It is relatively rare in most of its range, but more common in Bermuda. The rainbow parrotfish is widely harvested in subsistence fisheries in many parts of the Caribbean.